Power semiconductor module cooling apparatus

ABSTRACT

An IPM cooling apparatus includes a cooling unit having a cooling fluid channel, and a mounting unit fixed to the cooling unit. A wall portion of the cooling unit, which portion faces the cooling fluid channel, has a mounting surface on which the IPM is mounted. The mounting unit is composed of a heat transfer plate formed of a thermally conductive material and joined to the mounting surface of the cooling unit, and a male screw component which has a plate-like head portion and a male screw portion. The plate-like head portion is caused to bite into the lower surface of the heat transfer plate so as to form a recess on the lower surface. The late-like head portion is fitted into the recess formed on the lower surface such that the plate-like head portion does not project from the lower surface and is prevented from rotating.

BACKGROUND OF THE INVENTION

The present invention relates to a power semiconductor module cooling apparatus for cooling a power semiconductor module, such as an IGBT module or an intelligent power module, in which a semiconductor device and a control circuit therefor are integrated.

In recent years, a power device (semiconductor device) such as an IGBT (Insulated Gate Bipolar Transistor) used in a power converter mounted in an electric vehicle, a hybrid vehicle, an electric railcar, or the like has been frequently provided in the form of an IGBT module (hereinafter referred to as “IGBTM”) in which the power device is integrated with a control circuit and is accommodated in a common package together with the control circuit, or in the form of an intelligent power module (hereinafter referred to as “IPM”) in which the IGBTM is integrated with a protection circuit and is accommodated in a common package together with the protection circuit.

A cooling apparatus for cooling an IGBTM has been conventionally known (see Japanese Patent Application Laid-Open (kokai) No. H8-186209). The known cooling apparatus includes a refrigerant tank which is constituted by plate-like outer wall members and accommodates a refrigerant which boils upon receipt of heat generated from the IGBTM, and a heat radiation unit which is provided above the refrigerant tank and communicates with the refrigerant tank. The vapor-phase refrigerant ascending from the refrigerant tank is condensed to liquid within the heat radiation unit. Spacers having female screw holes are interposed between the mutually facing outer wall members of the refrigerant tank. The IGBTM is attached to the outer surface of the corresponding outer wall member by passing male screw components, which have been passed through screw insertion holes provided in the IGBTM, through the outer wall member, and screwing them into the female screw holes of the spacers.

However, in the cooling apparatus disclosed in the publication, since the male screw components penetrate the outer wall member of the refrigerant tank, there is a possibility that the refrigerant leaks from the refrigerant tank.

Meanwhile, a cooling apparatus for cooling a power device such as an IGBT which is not modularized has been known (see Japanese Patent Application Laid-Open (kokai) No. 2003-298009). This cooling apparatus includes a cooling unit which is composed of a heat radiation substrate and heat radiation fins integrally formed on one side of the heat radiation substrate, and an insulative circuit board which is composed of a ceramic plate, a porous metal layer provided on one side of the ceramic plate, and a metallic layer covering the surface of the porous metal layer. The surface of the ceramic plate of the insulative circuit board opposite the side where the porous metal layer is provided is mounted on the other side of the heat radiation substrate of the cooling unit via grease having high thermal conductivity. A peripheral edge portion of the ceramic plate is mounted to the heat radiation substrate via jigs fixed to the heat radiation substrate of the cooling unit. The jigs are fixed by screwing male screw components, which have been passed through screw insertion holes provided in the jigs, into female screw holes formed in the heat radiation substrate of the cooling unit. A plurality of power devices are soldered to the metallic layer of the insulative circuit board.

However, in the cooling apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-298009, the cooling unit is composed of a heat radiation substrate and heat radiation fins integrally formed on one side of the heat radiation substrate, and the plurality of power devices soldered to the metallic layer of the insulative circuit board are cooled by air which flows through spaces between the heat radiation fins. Therefore, the cooling efficiency of the cooling apparatus is insufficient.

Moreover, there has been known an improved cooling apparatus which cools an unmodularized power device such as an IGBT efficiently as compared with the cooling apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-298009 (see Japanese Patent Application Laid-Open (kokai) No. 2009-195912). This improved cooling apparatus includes a casing which is composed of a top wall, a bottom wall, and a peripheral wall and which has a cooling fluid channel therein; a corrugated heat radiation fin disposed in the fluid channel of the casing; an inflow pipe which is connected to the casing and through which a cooling liquid flows into the casing; an outflow pipe which is connected to the casing and through which the cooling liquid flows out of the casing; and an insulative circuit board joined to the outer surface of the top wall of the casing. The power device is joined to the insulative circuit board.

Incidentally, in the case where the cooling apparatus disclosed in the Japanese Patent Application Laid-Open No. 2009-195912 is applied to cooling of a power semiconductor module such as an IGBTM or IPM, the cooling apparatus must be modified such that, instead of joining the insulative circuit board to the outer surface of the top wall of the casing, the spacers disclosed in Japanese Patent Application Laid-Open No. H8-186209 are disposed in the casing of the cooling apparatus disclosed in Japanese Patent Application Laid-Open No. 2009-195912, and jigs are fixed to the casing by passing male, screw components, which have been passed through screw insertion holes provided in the power semiconductor module, through the top wall of the casing, and screwing them into the female screw holes of the spacers, whereby the power semiconductor module is attached to the casing via the fixed jigs. However, in this case, since the male screw components penetrate the top wall of the casing, there is a possibility that the cooling liquid leaks. Also, the spacers prevent the cooling liquid from smoothly flowing within the casing, to thereby lower the cooling efficiency. Moreover, since the spacers cannot be disposed in a region where the fin is present, the degree of freedom in disposing the power semiconductor module decreases.

A conceivable measure of solving the above-described problem which occurs when the cooling apparatus disclosed in Japanese Patent Application Laid-Open No. 2009-195912 is applied to cooling of a power semiconductor module is increasing the thickness of the top wall of the casing and forming female screw holes in the top wall of the casing into which male screw components are screwed. However, in such a case, the cooling efficiency may become insufficient due to a decrease in heat conduction from the power semiconductor module to the cooling fluid flowing within the casing.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above-mentioned problem and to provide a power semiconductor module cooling apparatus which can prevent leakage of cooling fluid and suppress lowering of cooling efficiency.

To achieve the above object, the present invention comprises the following modes.

1) A power semiconductor module cooling apparatus comprising:

a cooling unit having a cooling fluid channel provided therein; and

a mounting unit fixed to the cooling unit and used for mounting a power semiconductor module onto the cooling unit, wherein

at least a portion of the entire outer surface of a wall portion of the cooling unit, the wall portion having an inner surface facing the cooling fluid channel, serves as a mounting surface on which the power semiconductor module is mounted;

the mounting unit is composed of a heat transfer plate formed of a thermally conductive material and joined to the cooling unit along the mounting surface, and a male screw component which has a plate-like head portion and a male screw portion, the plate-like head portion being located on the side toward the cooling unit and the male screw portion extending through the heat transfer plate; and

the plate-like head portion of the male screw component is fitted into a recess formed on a surface of the heat transfer plate on the side toward the cooling unit such that the plate-like head portion does not project from the surface toward the cooling unit and is prevented from rotating about the axis of the male screw portion.

2) A power semiconductor module cooling apparatus according to par. 1), wherein the plate-like head portion of the male screw component is formed of a material harder than the heat transfer plate; the plate-like head portion of the male screw component is caused to bite into the surface of the heat transfer plate on the side toward the cooling unit, whereby the recess is formed on the surface of the heat transfer plate on the side toward the cooling unit, and the plate-like head portion of the male screw component is fitted into the recess such that the plate-like head portion does not project from the surface toward the cooling unit and is prevented from rotating about the axis of the male screw portion.

3) A power semiconductor module cooling apparatus according to par. 1), wherein a plurality of protrusions are integrally formed on a surface of the plate-like head portion of the male screw component, which surface faces toward the side where the male screw portion is present.

4) A power semiconductor module cooling apparatus according to par. 1), wherein the cooling unit includes a casing having the cooling fluid channel formed therein; a heat radiation fin is disposed in the cooling fluid channel within the casing; and at least a portion of the entire outer surface of a wall portion of the casing, the wall portion having an inner surface facing the cooling fluid channel, serves as the mounting surface on which the power semiconductor module is mounted.

5) A power semiconductor module cooling apparatus according to par. 1), wherein the heat transfer plate is formed of aluminum, and the male screw component is formed of aluminum which is harder than the aluminum forming the heat transfer plate.

6) A power semiconductor module cooling apparatus according to par. 1), wherein the heat transfer plate is formed of aluminum, and the male screw component is formed of an iron alloy which is harder than the aluminum forming the heat transfer plate.

7) A power semiconductor module cooling apparatus according to par. 1), wherein the heat transfer plate is formed of a copper alloy, and the male screw component is formed of an iron alloy which is harder than the copper alloy forming the heat transfer plate.

The power semiconductor module cooling apparatus of any of pars. 1) to 7) includes a cooling unit having a cooling fluid channel provided therein, and a mounting unit fixed to the cooling unit and used for mounting a power semiconductor module onto the cooling unit. At least a portion of the entire outer surface of a wall portion of the cooling unit, the wall portion having an inner surface facing the cooling fluid channel, serves as a mounting surface on which the power semiconductor module is mounted. The mounting unit is composed of a heat transfer plate formed of a thermally conductive material and joined to the cooling unit along the mounting surface, and a male screw component which has a plate-like head portion and a male screw portion, the plate-like head portion being located on the side toward the cooling unit and the male screw portion extending through the heat transfer plate. The plate-like head portion of the male screw component is fitted into a recess formed on a surface of the heat transfer plate on the side toward the cooling unit such that the plate-like head portion does not project from the surface toward the cooling unit and is prevented from rotating about the axis of the male screw portion. Therefore, a power semiconductor module can be mounted onto the mounting unit by passing the male screw portion of the male screw component of the mounting unit through a screw insertion hole provide in the power semiconductor module, and screwing a nut onto an end portion of the male screw portion. Since the male screw component does not penetrate the wall portion of the cooling unit, leakage of a cooling fluid from the cooling unit can be prevented. Further, the heat transfer plate is only required to have a thickness which enables formation of a recess into which the plate-like head portion of the male screw component is fitted. Therefore, as compared with the case where a female screw hole is formed in the top wall of the casing disclosed in Japanese Patent Application Laid-Open No. 2009-195912, the thickness of the top wall can be reduced. Accordingly, it is possible to suppress a decrease in heat conduction from the power semiconductor module to the cooling fluid flowing through the cooling fluid channel within the cooling unit, and suppress a decrease in cooling efficiency caused by the decrease in heat conduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a state in which IPMs are attached to a cooling apparatus according to the present invention;

FIG. 2 is an enlarged sectional view taken along line A-A of FIG. 1;

FIG. 3 is an enlarged partial view of FIG. 2;

FIG. 4 is a perspective view showing a state before a male screw component is attached to a heat transfer plate in a method of manufacturing the cooling apparatus of FIG. 1; and

FIG. 5 is a perspective view showing a modification of the male screw component.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will now be described with reference to the drawings. In this embodiment, a power semiconductor module cooling apparatus according to the present invention is applied to cooling of IPMs.

In the flowing description, the upper, lower, left-hand, and right-hand sides of FIG. 2 will be referred to as “upper,” “lower,” “left,” and “right,” respectively; and the right-hand side of FIG. 1 will be referred to as “front,” and the opposite side will be referred to as “rear.”

In the following description, the term “aluminum” encompasses aluminum alloys in addition to pure aluminum.

FIGS. 1 to 3 show a state in which IPMs are attached to the cooling apparatus according to the present invention. FIG. 4 shows one step of a method of manufacturing the cooling apparatus according to the present invention.

As shown in FIGS. 1 and 2, an IPM cooling apparatus 1 (power semiconductor module cooling apparatus) includes a cooling unit 2, and a mounting unit 3 which is fixed to the cooling unit 2 and which is used to mount a required number of IPMs I to the cooling unit 2.

The cooling unit 2 includes a casing 4 having a cooling fluid channel 5 formed therein; a heat radiation fin 6 formed of aluminum and disposed in the cooling fluid channel 5 within the casing 4; an aluminum inlet pipe 7 which is connected to the casing 4 and through which a cooling fluid flows into the casing 4; and an aluminum outlet pipe 8 which is connected to the casing 4 and through which the cooling fluid flows out of the casing 4.

The casing 4 is composed of a top wall 9, a bottom wall 11, and a peripheral wall 12. The casing 4 has a cooling fluid inflow portion 13 projecting frontward from a right end portion of a front edge portion thereof, and a cooling fluid outflow portion 14 projecting frontward from a left end portion of the front edge portion. The inlet pipe 7 is connected to the cooling fluid inflow portion 13. The outlet pipe 8 is connected to the cooling fluid outflow portion 14. The casing 4 is formed by brazing together an upper constituent member 15 and a lower constituent member 16, which are formed of aluminum. The upper constituent member 15 constitutes the top wall 9 and upper halves of the peripheral wall 12, the cooling fluid inflow portion 13, and the cooling fluid outflow portion 14. The lower constituent member 16 constitutes the bottom wall 11 and lower halves of the peripheral wall 12, the cooling fluid inflow portion 13, and the cooling fluid outflow portion 14. The casing 4 has an inlet header section 17 and an outlet header section 18. The inlet header section 17 is provided at the right end of the casing 4, communicates with the cooling fluid inflow portion 13, and extends over the entire length of the casing 4 with respect to the front-rear direction. The outlet header section 18 is provided at the left end of the casing 4, communicates with the cooling fluid outflow portion 14, and extends over the entire length of the casing 4 with respect to the front-rear direction.

The cooling fluid channel 5 of the casing 4 is provided between front and rear portions of the peripheral wall 12 and between the inlet header section 17 and the outlet header section 18 such that the cooling fluid flows from the right side toward the left side. The heat radiation fin 6 is a corrugated fin which has crest portions 6 a, trough portions 6 b, and connection portions 6 c connecting the crest portions 6 a and the trough portions 6 b. The heat radiation fin 6 is disposed in the cooling fluid channel 5 such that the longitudinal direction of the crest portions 6 a and the trough portions 6 b coincides with the left-right direction. The crest portions 6 a are brazed to the top wall 9 of the casing 4, and the trough portions 6 b are brazed to the bottom wall 11 of the casing 4. A mounting surface 19 on which the IPMs I are to be mounted is provided on the top wall 9 of the casing 4 of the cooling unit 2. Specifically, the entire outer surface of a portion of the top wall 9, the potion having an inner surface facing the cooling fluid channel 5, serves as the mounting surface 19.

The mounting unit 3 is composed of a heat transfer plate 21 and male screw components 22. The heat transfer plate 21, which is formed of a thermally conductive material having a thermal conductivity of about 150 to 450 W/mK, such as aluminum or copper (including copper alloy), is disposed on and brazed to the mounting surface 19 of the top wall 9 of the casing 4 of the cooling unit 2. Each of the male screw components 22 has a plate-like head portion 23, and a male screw portion 24 formed integrally with the plate-like head portion 23. The male screw portion 24 extends through the heat transfer plate 21 such that the plate-like head portion 23 is located on the side (lower side) toward the cooling unit 2. Reference numeral 25 denotes a layer of a brazing material used to braze the heat transfer plate 21 to the mounting surface 19 of the top wall 9. The male screw portions 24 of the male screw components 22 are inserted into through-holes 26 of the heat transfer plate 21 from the lower side thereof. The plate-like head portions 23 are fitted into recesses 28 formed on the lower surface 21 a (the surface on the side toward the cooling unit 2) of the heat transfer plate 21 such that the plate-like head portions 23 do not project toward the cooling unit 2 from the lower surface and are prevented from rotating about the axes of the male screw portions 24.

Example combinations of the materials of the heat transfer plate 21 and the male screw components 22 are shown in the following table.

Heat transfer Male screw plate components Combination 1 aluminum aluminum 2 aluminum iron alloy 3 copper alloy iron alloy

The aluminum listed in the table has a Vickers hardness of 10 to 250, the iron alloy (including stainless steel) listed in the table has a Vickers hardness of 50 to 700, and the copper alloy listed in the table has a Vickers hardness of 40 to 300. These materials are used in a combination determined such that the Vickers hardness of the male screw components becomes higher than that of the heat transfer plate.

The plate-like head portion 23 of each male screw component 22 (in the present embodiment, the entire male screw component 22 including the male screw portion 24) is formed of a material harder than the heat transfer plate 21, such as carbon steel or stainless steel. As shown in FIG. 3, the plate-like head portion 23 of the male screw component 22 is circular, and has a plurality of protrusions 27 integrally formed on the upper surface (the surface on the side toward the male screw portion 24) of the plate-like head portion 23 at predetermined intervals in the circumferential direction such that the protrusions 27 project upward from the upper surface. For example, a Sel Stud (trade name), which is a product of Sel Japan Co. Ltd., is used for the male screw components 22. When the plate-like head portions 23 of the male screw components 22 are caused to bite into portions of the lower surface 21 a of the heat transfer plate 21 around the through-holes 26, the recesses 28 are formed on the lower surface 21 a of the heat transfer plate 21, and the plate-like head portions 23 are fitted into the recesses 28 such that the plate-like head portions 23 do not project toward the cooling unit 2 from the lower surface 21 a and are prevented from rotating about the axes of the male screw portions 24. The number of the male screw components 22 is properly determined in accordance with the number of the IPMs I to be mounted onto the mounting unit 3.

The IPMs I are mounted onto the cooling unit 2 of the IPM cooling apparatus 1 as follows. The male screw portions 24 of the male screw components 22 of the mounting unit 3 are passed through screw insertion holes 29 of the IPMs I from the lower side. Subsequently, nuts 31 are screwed onto upper end portions of male screw portions 24 which project upward from the screw insertion holes 29. Thus, the IPMs I are mounted onto the cooling unit 2.

In the IPM cooling apparatus 1 having the above-described structure, a cooling fluid, which is liquid or gaseous, having flowed from the inlet pipe 7 into the inlet header section 17 through the cooling fluid inflow portion 13 diverges in the front-rear direction in the inlet header section 17, and flows leftward within the cooling fluid channel 5, while passing through the spaces between the adjacent connection portions 6 c of the heat radiation fin 6. The cooling fluid having flowed leftward within the cooling fluid channel 5 enters the outlet header section 18, and flows out to the outlet pipe 8 through the cooling fluid outflow portion 14. Heat generated by the IPMs I is conducted through the heat transfer plate 21, the top wall 9 of the casing 4, and the heat radiation fin 6, and reaches the cooling fluid flowing through the cooling fluid channel 5. Thus, the IPMs I are cooled.

A method of manufacturing the IPM cooling apparatus 1 will now be described with reference to FIG. 4.

First, the upper and lower constituent members 15 and 16 of the casing 4, each having a brazing material layer on the inner surface side, are formed by performing press work on an aluminum brazing sheet having a brazing material layer on at least one side of the sheet. The through holes 26, which are equal in number to the IPMs I to be mounted, are formed in the heat transfer plate 21 having a required size. Also, there are prepared the heat radiation fin 6 formed from an aluminum bare material or an aluminum brazing sheet having a brazing material layer on each of opposite sides thereof, and the male screw components 22, each having the plate-like head portion 23 and the male screw portion 24.

Subsequently, as shown in FIG. 4, the male screw portions 24 of all the male screw components 22 are passed through all the through-holes 26 of the heat transfer plate 21 from the side of the surface 21 a, which is to be brazed to the casing 4 of the cooling unit 2. Subsequently, the heat transfer plate 21 is supported by an unillustrated die from the side opposite the surface 21 a such that the male screw portions 24 projecting from the through-holes 26 of the heat transfer plate 21 are inserted into holes formed in the die. Subsequently, through use of an unillustrated punch, the plate-like head portions 23 of all the male screw components 22 are pressed against the die. Thus, the entire plate-like head portions 23, including the protrusions 27, are caused to bite into the surface 21 a of the heat transfer plate 21, which is to be brazed to the cooling unit 2. As a result, the recesses 28 are formed on the surface 21 a of the heat transfer plate 21, and the plate-like head portions 23 are fitted into recesses 28 such that the plate-like head portions 23 do not project toward the cooling unit 2 from the surface 21 a and are prevented from rotating about the axes of the male screw portions 24.

Subsequently, the upper and lower constituent members 15 and 16, the heat radiation fin 6, the inlet pipe 7, and the outlet pipe 8 are assembled together, and the heat transfer plate 21 of the mounting unit 3 is disposed on the outer surface of the top wall 9 of the upper constituent member 15 with a film of a brazing material interposed therebetween. All the components are provisionally fixed together by an appropriate jig, and are heated to a predetermined temperature within a furnace, whereby the upper and lower constituent members 15 and 16 are brazed together, the upper and lower constituent members 15 and 16 and the heat radiation fin 6 are brazed together, the upper and lower constituent members 15 and 16 and the inlet pipe 7 and the outlet pipe 8 are brazed together, and the upper constituent member 15 and the heat transfer plate 21 are brazed together. These brazing operations are performed simultaneously. Thus, the IPM cooling apparatus 1 is manufactured.

In the above-descried manufacturing method, in place of interposing the brazing material film between the top wall 9 of the upper constituent member 15 and the heat transfer plate 21, the upper constituent member 15 may be formed of an aluminum brazing sheet having a brazing material layer on each of the opposite sides thereof, or the heat transfer plate 21 may be formed of an aluminum brazing sheet having a brazing material layer on one side thereof such that the brazing material layer forms the surface 21 a to be brazed to the upper constituent member 15.

The male screw components 22 used in the present embodiment have the protrusions 27 formed on the plate-like head portions 23. However, such protrusions 27 are not necessarily required.

FIG. 5 shows a modification of the male screw components used in the mounting unit 3.

In the case of a male screw component 40 shown in FIG. 5, a plate-like head portion 41 is square, and the protrusions 27 are not formed on the surface of the plate-like head portion 41 located on the side toward the male screw portion 24. As in the case of the above-described male screw component 22, the plate-like head portion 41 of the male screw component 40 is caused to bite into a portion of the surface 21 a of the heat transfer plate 21 to be brazed to the cooling unit 2, the portion being located around the through-hole 26. As a result, the recess 28 is formed on the surface 21 a of the heat transfer plate 21, and the plate-like head portions 41 of the male screw component 40 is fitted into recess 28 such that the plate-like head portion 41 does not project toward the cooling unit 2 from the surface 21 a and is prevented from rotating about the axis of the male screw portion 24.

Notably, a plurality of protrusions may be integrally formed on the surface (on the side toward the male screw portion 24) of the plate-like head portion 41 shown in FIG. 5 at predetermined intervals in the circumferential direction of the male screw portion 24. Also, in the male screw component 40 shown in FIG. 5, the shape of the plate-like head portion 41 is not limited to the square shape, and may be any of other polygonal shapes.

In the above-described embodiment, the power semiconductor module cooling apparatus of the present invention is applied to cooling of IPMs. However, the application of the present invention is not limited thereto, and the present invention can be applied to cooling of IGBTMs or other power semiconductor modules. 

What is claimed is:
 1. A power semiconductor module cooling apparatus comprising: a cooling unit having a cooling fluid channel provided therein; and a mounting unit fixed to the cooling unit and used for mounting a power semiconductor module onto the cooling unit, wherein at least a portion of the entire outer surface of a wall portion of the cooling unit, the wall portion having an inner surface facing the cooling fluid channel, serves as a mounting surface on which the power semiconductor module is mounted; the mounting unit is composed of a heat transfer plate formed of a thermally conductive material and joined to the cooling unit along the mounting surface, and a male screw component which has a plate-like head portion and a male screw portion, the plate-like head portion being located on the side toward the cooling unit and the male screw portion extending through the heat transfer plate; and the plate-like head portion of the male screw component is fitted into a recess formed on a surface of the heat transfer plate on the side toward the cooling unit such that the plate-like head portion does not project from the surface toward the cooling unit and is prevented from rotating about the axis of the male screw portion.
 2. A power semiconductor module cooling apparatus according to claim 1, wherein the plate-like head portion of the male screw component is formed of a material harder than the heat transfer plate; the plate-like head portion of the male screw component is caused to bite into the surface of the heat transfer plate on the side toward the cooling unit, whereby the recess is formed on the surface of the heat transfer plate on the side toward the cooling unit, and the plate-like head portion of the male screw component is fitted into the recess such that the plate-like head portion does not project from the surface toward the cooling unit and is prevented from rotating about the axis of the male screw portion.
 3. A power semiconductor module cooling apparatus according to claim 1, wherein a plurality of protrusions are integrally formed on a surface of the plate-like head portion of the male screw component, which surface faces toward the side where the male screw portion is present.
 4. A power semiconductor module cooling apparatus according to claim 1, wherein the cooling unit includes a casing having the cooling fluid channel formed therein; a heat radiation fin is disposed in the cooling fluid channel within the casing; and at least a portion of the entire outer surface of a wall portion of the casing, the wall portion having an inner surface facing the cooling fluid channel, serves as the mounting surface on which the power semiconductor module is mounted.
 5. A power semiconductor module cooling apparatus according to claim 1, wherein the heat transfer plate is formed of aluminum, and the male screw component is formed of aluminum which is harder than the aluminum forming the heat transfer plate.
 6. A power semiconductor module cooling apparatus according to claim 1, wherein the heat transfer plate is formed of aluminum, and the male screw component is formed of an iron alloy which is harder than the aluminum forming the heat transfer plate.
 7. A power semiconductor module cooling apparatus according to claim 1, wherein the heat transfer plate is formed of a copper alloy, and the male screw component is formed of an iron alloy which is harder than the copper alloy forming the heat transfer plate. 